This invention relates to fastening mechanisms, specifically to such nail or staple fastening mechanisms that require operation as a hand tool. This invention relates generally to an electromechanical fastener driving tool. Such devices are less than 15 pounds and are completely suitable for an entirely portable operation.
Contractors and homeowners commonly use power-assisted means of driving fasteners into wood. These can be either in the form of finishing nail systems used in baseboards or crown molding in house and household projects, or in the form of common nail systems that are used to make walls or hang sheathing onto same. These systems can be portable (not connected or tethered to an air compressor or wall outlet) or non-portable.
The most common fastening system uses a source of compressed air to actuate a cylinder to push a nail into the receiving members. For applications in which portability is not required, this is a very functional system and allows rapid delivery of nails for quick assembly. It does however require that the user purchase an air compressor and associated air-lines in order to use this system.
Thereafter, inventors have created several types of portable nail guns operating off of fuel cells. Typically these guns have a cylinder in which a fuel is introduced along with oxygen from the air. The subsequent mixture is ignited with the resulting expansion of gases pushing the cylinder and thus driving the nail into the work pieces. Typical within this design is the need for a fairly complicated assembly. Both electricity and fuel are required as the spark source derives its energy typically from batteries. In addition, it requires the chambering of an explosive mixture of fuel and the use of consumable fuel cartridges. Systems such as these are already in existence and are sold commercially to contractors under the Paslode name.
There are other nail guns that are available commercially, which operate using electrical energy. They are commonly found as electric staplers and electric brad tackers. The normal mode of operation for these devices is through the use of a solenoid that is driven off of a power cord that is plugged into a wall outlet. One of the drawbacks of these types of mechanisms is that the number of ampere-turns in the solenoid governs the force provided by a solenoid. In order to obtain the high forces required for driving brads and staples into the work piece, a larger number of turns are required in addition to high current pulses. These requirements are counterproductive as the resistance of the coil increases in direct proportion to the length of the wire in the solenoid windings. The increased resistance necessitates an increase in the operational voltage in order to keep the amps thru the windings at a high level and thus the ampere-turns at a sufficiently large level to obtain the high forces needed to drive the nail. This type of design suffers from a second drawback in that the force in a solenoid varies in relation to the distance of the solenoid core from the center of the windings. This limits most solenoid driven mechanisms to short stroke small load applications such as paper staplers or small brad tackers.
The prior art teaches three additional ways of driving a nail or staple. The first technique is based on a multiple impact design. In this design, a motor or other power source is connected to the impact anvil thru either a lost motion coupling or other. This allows the power source to make multiple impacts on the nail thus driving it into the work piece. There are several disadvantages in this design that include increased operator fatigue since the actuation technique is a series of blows rather than a continuous drive motion. A further disadvantage is that this technique requires the use of an energy absorbing mechanism once the nail is seated. This is needed to prevent the heavy anvil from causing excessive damage to the substrate. Additionally, the multiple impact designs normally require a very heavy mechanism to insure that the driver does not move during the driving operation.
A second design that is taught includes the use of potential energy storage mechanisms in the form of a spring. In these designs, the spring is cocked (or activated) through an electric motor. Once the spring is sufficiently compressed, the energy is released from the spring into the anvil (or nail driving piece) thus pushing the nail into the substrate. Several drawbacks exist to this design. These include the need for a complex system of compressing and controlling the spring and the fact that the force delivery characteristics of a spring are not well suited for driving nails. As the nail is driven into the wood, more force is needed as the stroke increases. This is inherently backwards to a springs unloading scheme in which it delivers less force as it returns to its zero energy state.
A third means for driving a fastener that is taught includes the use of flywheels as energy storage means. The flywheels are used to launch a hammering anvil that impacts the nail. This design is described in detail in U.S. Pat. Nos. 4,042,036, 5,511,715 and 5,320,270. The major drawback to this design is the problem of coupling the flywheel to the driving anvil. This prior art teaches the use of a friction clutching mechanism that is both complicated, heavy and subject to wear. This design also suffers from difficulty in controlling the energy left over after the nail is driven. Operator fatigue is also a concern as significant precession forces are present with flywheels that rotate in a continuous manner. An additional method of using a flywheel to store energy to drive a fastener is detailed in British Patent # 2,000,716. This patent teaches the use of a continuously rotating flywheel coupled to a toggle link mechanism to drive a fastener. This design is limited by the large precession forces incurred because of the continuously rotating flywheel and the complicated and unreliable nature of the toggle link mechanism.
All of the currently available devices suffer from a number of disadvantages that include:
1. Complex design. With the fuel driven mechanisms, portability is achieved but the design is complicated. Mechanisms from the prior art that utilize rotating flywheels have complicated coupling or clutching mechanisms based on frictional means. Devices that use springs to store potential energy suffer from reliability and complicated spring compression mechanisms.
2. Noisy. The ignition of an explosive mixture to drive a nail causes a very loud sound and presents combustion fumes in the vicinity of the device. Multiple impact devices are fatiguing and are noisy.
3. Complex operation. Combustion driven portable nail guns are more complicated to operate. They require fuel cartridges that need to be replaced and the combustion chamber must be cleaned.
4. Use of consumables. Combustion driven portable nail gun designs use a fuel cell that dispenses a flammable mixture into the piston combustion area. The degree of control over the nail driving operation is very crude as you are trying to control the explosion of a combustible mixture.
5. Non-portability. Traditional nail guns are tethered to a fixed compressor and thus must maintain a separate supply line.
6. Using a spring as a potential energy storage device suffers from unoptimized drive characteristics. Additionally springs are often not rated for these types of duty cycles leading to premature failure.
7. The flywheel type storage devices suffer from significant precession forces as the flywheels are kept rotating at high speeds. This makes tool positioning difficult. The use of counter-rotating flywheels as a solution to this issue increases the complexity and weight of the tool.
8. Need for precise motor control for repeatable drives. Flywheel designs that throw an anvil are very susceptible to damage in dry fire conditions.
In accordance with the present invention, a fastening tool is described which derives its power from a low impedance electrical source, preferably rechargeable batteries, and uses a motor to drive a kinetic energy storage mechanism which is directly coupled to a fastener driving mechanism and drives a fastener into a substrate. Upon receipt of an actuation signal from an electrical switch, an electronic circuit connects a motor to the electrical power source. The motor is coupled to a kinetic energy storing mechanism, such as a flywheel, preferably through a speed reduction mechanism. In the description of this invention, the words kinetic energy storage mechanism and flywheel may be used interchangeably. Both the motor and the flywheel begin to spin. When the flywheel hits a certain rotational velocity or within a prescribed amount of time or within a certain number of revolutions, the flywheel is directly coupled to a fastener driving mechanism that drives the anvil through an output stroke. The preferred fastener driving mechanism is a linkage system which converts rotational motion to linear motion in a harmonic fashion and more preferably a slider crank style mechanism. In the description of this invention, the words slider crank and harmonic motion mechanism may be used interchangeably. The clutching mechanism is a mechanical lockup design that preferably includes a drive pin which rotates with the kinetic energy storage mechanism. The position of the drive pin is determined in response to both electrical and mechanical elements which allow for rapid and positive engagement and disengagement of the fastener driving mechanism to the energy stored in the flywheel. A sensor indicates at least one position of the fastener driving mechanism and can be used to coordinate the engagement of the drive pin or its disengagement. Additional sensors or timers associated with this sensor can be used to coordinate completion of the driving stroke with subsequent disconnection of the motor from the power source. Once the motor is disconnected from the power source, the kinetic energy storage mechanism can either come to a stop on its own or a brake can be used to stop the mechanism very quickly. The preferred mode for the braking mechanism, if used, is dynamic braking from the motor. The drive pin engagement is designed to be electrically controlled, such as with a solenoid, to increase the robustness of the design. The disengagement of the drive pin can be either by electrical or mechanical means. One such mechanical means would be to position a stationary cam substantially after the nail driving stroke has been completed. Upon revolution of the kinetic energy storage mechanism past the stationary cam, the drive pin is repositioned back to its disengagement position. Upon completion of the drive cycle, the fastener driving mechanism moves back to its starting position via an elastic biasing means such as a spring at which point the cycle is considered complete.
Accordingly, in addition to the objects and advantages of the portable electric nail gun as described above, several objects and advantages of the present invention are:
1. To provide a sensing element and control scheme that determine when the faster driving mechanism has begun a driving cycle, completed a cycle and is ready to initiate the next cycle.
2. To provide motor reversal for improved handling of jamb conditions during the nail driving stroke.
3. To provide a fastener driving mechanism that has low reciprocated inertia during the nail drive.
4. To provide a fastener driving device which uses an elastic means to return the fastener driving mechanism to its starting position thus simplifying the design.
5. To provide a fastener driving device that uses a positive acting clutch such as a drive pin which directly couples the flywheel to the fastener driving mechanism thus reducing frictional wear.
6. To provide a reciprocating driver which follows a hamonic displacement during the drive cycle thus providing controlled conversion of rotational to linear motion and decreasing sensitivity to dry fire (no fastener) conditions.
7. To provide an electrical clutching means for moving the drive pin to an engagement position.
8. To provide a clutching means which uses a stationary cam to ensure that the drive pin is retracted and a moving cam to ensure that the solenoid is retracted to eliminate double firing.
9. To provide a fastener driving mechanism which has compliance during impact and during its engagement positions thus reducing wear.
Further objects and advantages will become more apparent from a consideration of the ensuing description and drawings.